So for some reason, I'm getting 6.7 Mpg city......, I drive a 2012 Infiniti G37 Coupe X AWD I have no check engine lights at all. I changed my spark plugs, engine oil, brakes,/rotors, and transmission oil still nothing. I have an after-market intake and exhaust installed but it was installed after I noticed the poor fuel economy. I don't think that's the cause of the poor fuel economy. The exhaust is an Invidia Catback exhaust and a Weapon R short ram cold air intake. Also, my location is NYC, and there is a lot of stop-and-go

traffic. Please help any suggestions would be amazing. I'm driving a tank at this point and gas is expensive as hell nowadays.

 

Well, previous records show the car was capable of efficiency then something happened and it started guzzling.

Most faulty systems would have thrown a CEL light. For now you should back off the pedal a bit in the city, throw it on Neutral while at the lights and run without AC while accelerating to see if your numbers improve.

This low of a number is usually attributed to lead foot city driving with all accessories on. Get yourself a OBD reader, this will show what numbers you're actually seeing during cruise.

It's possible you have a bad O2 sensor fooling the car into a rich parameter which wont trigger a light sometimes.